1. Field of the Invention
The present invention relates to a thermistor type temperature sensor and, more particularly, to a wide-range thermistor type temperature sensor.
2. Description of the Related Art
In recent years, there have been increasing demands for a temperature sensor with high reliability and high precision. A thermistor element 111 is shown in FIG. 10 as a conventional thermistor type temperature sensor used in high temperature regions. Electrode wires 491 and 492 are connected to the end portions of the thermistor element 111, which is buried in an insulating ceramic 512 and housed in a metallic protective tube 51. Temperature is computed by measuring the resistance value thereof from a lead terminal 511.
In another known high-temperature thermistor element which is disclosed in, for example, Japanese Patent Laid-Open No. 63-78503, a thermistor is buried in an oxide ceramic layer, and formed into an integral unit.
However, it is necessary to house a plurality of thermistor elements each having a different temperature measurement range in order to widen the temperature measurement range of the thermistor type temperature sensor to form a wide-range thermistor type temperature sensor.
However, in the conventional thermistor type temperature sensor, shown in FIG. 10, having a thermistor element housed in a metallic protective tube, a plurality of thermistor elements must be housed therein, causing the problem, for example, that the size of the temperature sensor itself becomes bigger. In addition, heat capacitance becomes large because of the enlargement of the temperature sensor itself, and the internal temperature distribution becomes non-uniform. Consequently, the responsiveness of the thermistor type temperature sensor becomes markedly worse, causing another problem, in that the accuracy of measured temperatures decreases. If, however, the thermistor type temperature sensor is unreasonably miniaturized, durability in high temperatures decreases considerably because each thermistor element is formed into a thin member.